Cant post follow up question. UI thinks model is still answering

I ask GPT-5 a first message. It answer, then I want to post a follow-up question. But I cannot. I can type my question in the input-box. But when I press ‘enter‘ nothing happens.
When I then look at the UI.

The input-box still think GPT-5 is still answering the previous question even though the model is ready.

Solution is to press Stop. Then I can submit my follow-up question